The invention is directed to an electro-optical hand-held distance measuring instrument with a modulated laser measurement beam.
In the construction or building industry, it is necessary to determine distances up to several hundred meters with an accuracy of within a few millimeters. In order to measure distance, the hand-held distance measuring laser devices designed for this purpose generally use a method which measures the difference in phase velocity of a modulated visible laser beam as a means for optical distance measurement in that a measurement beam, preferably the visible laser beam of a laser diode, which is bundled by collimating optics is directed to the surface of an object to be measured. The optical radiation which is backscattered or reflected by the light spot of the measurement beam that is positioned on the object to be measured is focused on the active surface of a measuring photodetector by a reception lens. For distance measurement, the measurement beam of the laser diode is generally modulated in intensity, i.e., a measurement signal is superimposed on the light beam. The signal transit time (or signal phase shift) from the optical transmitter through the measurement object to the detector is determined by an evaluating unit from the signal, which is backscattered or reflected by the measurement object received by the measurement photodetector and processed by the receiver electronics. Finally, the measured distance is given by the signal transit time and the light velocity. Distance measurement always requires an opposite surface, which is usually not available in the building industry when measuring or breaking down into lengths in the plane of walls or floors.
According to DE19836812A1, an electro-optical hand-held distance measuring instrument has a housing which can be held in the hand and an electro-optical distance measurement module with an electric beam source for generating an optical measurement beam, a beam receiver, a display, and an operator control. In addition, aside from simple measurement of distance, it has several additional calculation functions such as measurement of surfaces and volumes and the addition and subtraction of distances. Very short distances from 0 to 20 cm cannot be measured directly due to the length of the housing of the electro-optical hand-held distance measuring instrument extending in front in the measurement beam direction. These electro-optical hand-held distance measuring instruments are not always available to the user particularly in the building industry, but are generally only brought along for special tasks that have been planned in advance.
In order to measure distances from 0 to 2 m, a mechanical distance measuring device with an optically readable measurement scale is generally used. Further, mechanical distance measuring devices such as the measuring tape and folding measuring ruler are small, handy and do not require a target surface. Generally, distances of up to 5 m are measured with measuring tape. The folding ruler (measuring stick, double meter, meter rod), an obligatory accouterment of special groups of professionals in the building industry that is always on hand when distance is to be measured, is a particularly popular and indispensable tool of long standing especially when measuring arms-length distances due to the fact that measurements can be carried out simply and quickly. In addition, it is easy to make marks on walls and floors and to measure or plot virtual structural component parts (in the air, as it were). With mechanical instruments for measuring distance, subjective reading errors which are caused by objective soiling of the measurement scale or faulty counting depending on the viewing angle occur as absolute measurement errors. At distances of several meters, distance-dependent measurement errors result in particular from a poorly defined placement or measurement point, slack or sagging in the distance measuring device, pushing or pulling forces, as well as aging, moisture and thermal expansion of the distance measuring device. The accuracy of a distance measurement of within a few millimeters, which is at least occasionally necessary in the building industry is not ensured with the mechanical distance measuring devices that are generally all that is available.
According to DE 19916409, a folding measurement rod comprises ten elongated, inherently rigid members with a length of up to 23 cm, which are connected to one another in a lockable manner to be rotationally swivelable alternately at their respective ends. At least one optically readable measurement scale for distances extends along an area, which swivels out along a line. This measurement scale usually is divided into millimeters or inches and arranged on a front end of the folding measurement rod designed as a reference point and beginning with zero.
According to U.S. Pat. No. 5,713,135, U.S. Pat. No. 5,894,675, various mechanical measuring gauges for the building industry are combined with a laser pointer for exact positioning. According to US20020193964, a hand-held distance measuring instrument has a measuring tape which is coiled up in a housing that can be held in the hand for measuring distances and a laser pointer as optical pointer. The laser beam is not designed as a measurement beam. In addition, there are no reception optics.